Heat treatment of magnetic metal bodies



July 27 1926. v 1 1,594,322

D. S. ODONOVAN HEAT TREATMENTDF MAGNETIC METAL BODIES Filed Dec. 5, 1924 2 Sheets-Sheet 1 Lwerxiifl July 27 1926. 1,594,322

D. S. ODQNQVAN HEAT TREATMENT OF MAGNETIC METAL BODIES Filed Dec. 5, 1924 2 Sheets-Sheet 2 Patented July 27, 1926.

UNITED STATES DAVID STANISLAUS ODONOVAN, 0F VOGELFONTEIN, TRANSVAAL, SOUTH AFRICA.

HEAT TREATMENT OF MAGNETIC METAL BODIES.

Application filed December 5, 1924, Serial No This invention has reference to the heat treatment of material and particularly to the heat treatment of rock drill tools.

A purpose of the invention is to subject an unhardened portion of a steel body to heat treatment without detriment to a hardened part of the same; a particular application of this feature of the invention being to the normalizing of the stems of rock drills whilst maintaining the hardness of the shank thereof.

A further purpose is to control the heat treatment according to the magnetic properties of the heated material in a manner suitable to the treatment of localized portions of bodies other than the ends.

A specific object of the invention is to effect the normalizing of drill stems in large quantities and in the minimum of time, coupled with automatic control which ensures equal and correct treatment of each drill.

The invention consists in the process and apparatus hereafter described and claimed.

Apparatus according to the invention is illustrated in the accompanying drawings in which,

Fig. I is a projected view, partly sectioned, of a furnace for normalizing drill steel in quantities.

Fig. II is a vertical section through a magnet casing.

Fig. III is a wiring diagram.

Fig. IV is an enlarged view of a portion of the conveyor.

Fig. V shows one of the blocks for the conveyor turned onto its side.

Fig. VI shows a rock drill tool.

The articles which the furnace illustrated is intended to treat are rock drill tools, of.

which an example is shown in Fig. VI. Such a drill consists of a rod 2 of tool steel forged at one end to form the cutting point 3 and having the shank 4- shaped suitably to be struck by the hammer piston of a drilling machine and to be engaged rotatively by said machine. This shank 4 is often of square section as shown and provided with a collar 5 for limiting its penetration into the drilling machine. Its extremity 6 is hardened to resist deformation by the blows to which it is subjected in use.

Such rock drilling tools are very liable during use to fracture in the stem at about the point marked A. This may however be overcome if said part of the stem is periodically normalized, that is heated to decales- 754,141, and in South Africa January 29, 1924.

is so treated whilst keeping the shank 4 suf-' ficiently cool to maintain its hardness, thus saving the expense and labour of subsequently re-hardening the shank.

Other bodies having hardened and unhardened parts may similarly have an unhardened part heat treated as stated whilst keeping the hardened part from being detrimentally heated.

The invention further consists in regulating the heat treatment automatically by passing the drills or other material through a heating zone, testing the magnetic properties of the material prior to its withdrawal from the heating zone and regulating the withdrawing movement according tothe result of such test.

Referring to the drawings, the general features of the furnace designed for carrying out the above described operations, comprise a long narrow and high heating chamber 7 through which the drills 2 are moved by a conveyor 8 driven by a motor 9. The drills are carried in line and in an upright position, shanks downwards. They enter the chamber at the end 10 and leave at the end 11.

Towards the outgoing end of the chamber the drills pass before the magnets 12, 13, 1.4. These magnets test the magnetic properties of the drills and so govern the motor 9 as either to slow down or stop the conveyor if the drills are insufficiently heated or to accelerate the conveyor to prevent the drills from being overheated.

The furnace illustrated is coal fired and comprises the two fire grates 15, one at each side. From each of these grates the prodnets of combustion are conducted to one end" of a flue 16 which extends to the other end of the furnace. Outside of each of said flues 16 and parallel with the same is abypass flue 17 from which several openings 18 lead to the main flue. Before each such opening there is arranged in the flue 17 a damper 19 which controls the amount of gas which is passed to said opening. From the farther end of the flue 16 the gases pass through an opening 20 to a return flue 21 above the fiue 16 and thence to a chimney 22.

The heating chamber 7 is provided by the space between the opposite flues 16, 16 and 21, 21. It is roofed in at 23 and its ends are roughly closed by easily displaceable closures, such as the chain curtains 24, in order to prevent draughts. The inner walls of the flues 16 are made of metal plate so as to transmit h at from the gases in the flues 16 to the lower part of the chamber 7. The direction of travel of the gases is such as to roduce in the lower part of the chamber l a temperature gradient rising from the end 10 at which the drills enter, so that the drills are heated gradually without sudden exposure to a detrimental temperature. The temperature gradient may be adjusted by manipulating the dampers 19.

The conveyor comprises the two end sprocket wheels 26, one of which is driven by the electric motor 9 through gearing 27 The sprockets drive a chain consisting of links 28 and pins 29, the latter of which are fitted with wheels 30 running in channels 31 which guide and support the chain. I

Secured to each link is a trough section 32. (inc end 33 of each trough section is socketed to lit the end 34 of the next trough section so hat in the straight part of the chain the several trough sections form a continuous trough extending from one sprocket to the other. l/Vater is fed into this trough at one end by a pipe 35 and runs to the other end for the purpose of keeping cool the shank ends of the drills as herea'lter described, the direction of flow of the water being opposite to the direction of travel of the drills.

In each trough is fitted a block 36 formed with a number of vertical socket holes 37 into which the drill shanks are titted in order to support the drill in an upright position and also in order to keep the shank end cool, the sockets being round, square or of other cross section to fit the shank.

The blocks slip under lugs 38 at the end of each trough section, whereby they are retained in position while their trough sections are on the upper straight portion oi the conveyor, but can tall out or the trough sections as the latter turn over the sprocket at the outgoing end of the conveyor.

The blocks are spaced away from the sides of the containing trough sections by ribs 39 and from the bottom by ribs 40, so that water can Jirculate about the blocks to keep them cool. The ribs 40' slightly cover the lower ends of the socket holes 37, thereby keeping the extremities 6 of the drills in position to be directly bathed by the cooling water.

The magnets 12, 13, 14 are positioned to extend through the intake to one of the tines l6 and into the hot end or said flue 16, so that their active ends are near to the drills when the latter are most highly heated.

Each magnet is mounted in a frame 41 which removably fits n a water jacket 42 through which cooling water is circulated by the pipes 43. The magnet is hung from the frame 41 by chains 44 which permit it to swing towards and from the drills; and a light spring 45 tends to hold it retracted from the drills. The windings 46 of the several magnets are connected by leads 47 to the mains 48 through the controlling rheostat 49.

Secured to the rear end of the magnet 12 is one element 50 of an electric switch, the other element 51 of which is fixed. When the magnet 12 is retracted by its spring 45 the switch 50, 5.1 is closed, energizing the relay 52 and closing the switch 53 in the leads 54 to the motor 9. When the magnet swings forward towards the drills, the switch 50, 51 is opened. de-energizing the relay 52 which opens the switch 53 and stops the motor.

A similar switch 55 is fitted to the magnet 13. When this magnet swings back it opens the switch 55, and (lo-energizes the relay 56 so opening tne switch 57. The latter in turn cuts in a. resistance 58 and so causes the shunt wound motor 9 to be accelerated. The magnet 14 is provided with a switch 59 and connection similar to those for the magnet 13, which have the effect of cutting in a further resistance 60 and so accelerating the motor more than the magnet 13.

In operating the furnace the conveyor is started and water is turned on to flow through the upper conveyor troughs. Blocks 36 suitable for the drills to be treated are slipped into the conveyor trough sections at the intake end of the furnace. Drills 2 are inserted into said blocks and thus carried through the furnace, the lower ends of their stems being thereby gradually heated.

The magnets 12, 13, 14 are energized and the heated drills pass before them prior to being discharged from the furnace Should the drill or drills which come within the effective magnetic field of the magnet 12, be insufiiciently heated and therefore magnetic, they and the magnet attract one another, the magnet moves against its spring 45 and towards the drills and thereby opens the switch 50, 51. The motor is thereby stopped until the drills increase in temperature sufficiently to become non-magnetic, whereupon the magnet 12 is withdrawn by its spring, recloses the switch 50, 51 thereby causing the starting oi the motor and setting the drills in motion once more.

The magnets 13, 14 on the other hand operate to accelerate the motor. The steel which passes them is normally not fully heated and is magnetic. They are accordingly attracted towards the drills against their springs 45 and their switches 55, 59 are thereby normally kept open. If the drills are already nonmagnetic upon reach ing the effective field of the magnet 13 said non-magnetic when it reaches the eifective cutting in resistance 58 and causing the motor to be accelerated. If the steel is already non-magnetic when it reaches the effective field of the magnet 14, said magnet similarly falls back cutting in more resistance and further accelerating the motor. Both the switches 55, 59, however are subservient to the switch 50, 51; the efiect being that no drill is'passed out until it is heated to the proper temperature. I

In the case of alloy steel or low carbon steel, the loss of magnetism is not an exact indication that the steel has been properly heated, the decalescence temperature being higher than the temperaturev at which magnetism totally disappears. Accordingly for the treatment of such steel, the magnets are shifted somewhat towards the cooler end of the turnace,'by a distance such that after passing the magnets the steel remains in the eating Zone for a further period suflicient to bring it to decalescence before discharge from the furnace.

To ensure the cooling of the drills with the necessary rapidity to bring about the toughest condition of the metal, they may. be sprayed, u on emerging from the heating chamber, y liquid dropped onto them from the pipe 61. a

In the foregoing description of the operation attention has been directed particularly to the temperature of decalescence of the steel; but it will be evident that by suitably co-ordinating the magnetic strength of the magnets and the retractive force of their springs 45 the automatic control may be adjusted to the attainment of any desired temperature above that at which the material under treatment begins to lose magnetism. This feature may be utilized for example by first bringing the steel to decalescence, hardening by quenching'it rapidly in water, and then drawing the temper by passing it through the same or another similar furnace in which the magnets are set to operate at the necessary lower temperature.

I claim:

1. The process of heat treating a steel rock drill tool having an unhardened stem and a hardened shank, which consists in heating the stem to the temperature of decalescence while bathing the shank with a cooling fluid, and thereafter cooling the stemat the proper rate to leave the metal of the stem in the sorbitic condition.

2. The process of heat treating a steel rock drill having an unhardened stem and a hardened shank. which consists in heating the stem to decalescence whilst keeping the shank substantially unheated, and thereafter cooling the stem at the necessary rate to leave the steel in the sorbitic condition.

3. The process which consists in traversing magnetic properties while it is in said zone I and controlling its continued traversing movement by the etlect of such testing.

4. Theprocess which consists in moving a body through a graduated heating zone from a region of low temperature to a region of high temperature, testing its magnetic propertie while in the region of high temperature and controlling its continued movement by the result of such testing.

The process which consists in moving a body through a heating zone, subjecting it at one stage of its movement to one magnetic test, and at a later stage to a second magnetic test and accelerating or retarding its movement according to the manner in which it answers said tests res ctively.

6. A furnace comprising a heating chamber, motor mechanism for conveying material from the chamber, and means for testing the magnetic properties of material in the chamber, said means controlling the motor mechanism.

7. Combination of a heating chamber, motor mechanism for conveying material from the chamber, movable magnet means arranged to react with material in the chamber, movement of the magnet means controlling the motor mechanis 8. The combination of a heating chamber, motor mechanism for moving material through the chamber, magnet means arranged to react with the material at one stage of its movement and controlling the motor mechanism to accelerate movement thereof, and further magnet means arranged to react with the material at a later stage of its movement and controlling the motor mechanism to retard movement thereof.

9. The combination of a heating chamber, motor mechanism for moving material through the same, and a control magnet' adapted to react with the material about to pass out of the chamber and controlling the motor mechanism to prevent 'the withdrawal of material insufiiciently demagnetized.

10. The combination of a heating chamber, a conveyor constructed to receive and carry through the chamber a number of similar articles in line, a motor operating the conveyor, and magnetic means reacting with the articles at the exit end of the chamber and controlling the motor. a u

11. A furnace comprising a long narrow heating chamber, a conveyor constructed to receive a number of dr ll steels in line and in an upright position and in single-file and to convey them thus through the chamber, and means to control the movement of the conveyor according to the magnetic condition of the steel.

12; A furnace comprising a long narrow heating chamber, means to heat the same with a temperature gradient rising from the a body througha heating zone, testing its entrance end of the same to the exit end thereof, a conveyor constructed to receive a number of drill steels in an upright position and in line, and arranged to convey them thus through the heating chamber from the entrance end to the exit end of the same, a motor driving the conveyor, and temperature influenced means arranged at the exit end of the furnace and controlling the motor.

13. A furnace comprising a high, long and narrow heating chamber, a main flue running along each side of the same near its lower end, a heat conducting wall separating each such flue from the heating chamber, a by-pass flue running parallel with each flue remotely from the heating chamber, regulatable means for admitting combustion products from the by-pass fiues to the main flues, means for admitting combustion products to the ends of all the lines at one end of the furnace, means for conveying material through the heating chamber, and means for regulating the speed at which material is so conveyed. I

- 14. A drill heating furnace comprising a heating chamber, a conveyor for carrylng drills therethroug'h, and removable blocks in the conveyor apertured to receive drill shanks.

15. A furnace comprising a heating chamher, a conveyor for carrying articles through the chamber, said conveyor providing a continuous trough and means for passing water through the trough oppositely to the direction of travel of the conveyor.

16. A furnace comprising a long narrow heating chamber, means to heat a local zone of said chamber of limited height, a conveyor constructed to receive a number of elon- In testimony whereof I have hereunto set I my hand.

DAVID STANISLAUS ODONOVAN. 

